Recently, the rapid development of smaller, lighter, and higher performance communication and other electronic equipment has required the development of high performance and large capacity batteries to power such equipment. The demands for high energy density batteries have fostered investigation of rechargeable lithium batteries. Positive active materials for rechargeable lithium batteries use lithium-transition metal oxides, and negative active materials use crystalline or amorphous carbonaceous materials or carbon composites. The active materials are coated on a current collector with a predetermined thickness and length, or they are formed as a film, to produce electrodes. The electrodes, together with a separator, are wound or stacked to produce an electrode assembly and the electrode assembly is inserted into a battery case, such as a can, followed by insertion of an electrolyte to fabricate a battery.
The electrolyte generally includes a lithium salt and one or more organic solvents. The organic solvents generally include from two to five solvents which may include cyclic carbonates such as ethylene carbonate and propylene carbonate, and linear carbonates such as dimethyl carbonate, ethylmethyl carbonate, and diethyl carbonate. Such organic solvents are highly reactive for a negative electrode and are liable to be decomposed by reacting with the negative electrode during cell operation resulting in the generation of a large amount of gas during charge and discharge. This can cause a reduction in cell stability.